The ratio of the measured molar volume of a real gas to the measured molar volume if the gas were to behave ideally is known as​

compressibility

Explanation:

The ratio of the measured molar volume of a real gas to the measured molar volume  of an ideal gas is known as​ compressibility.

Compressibility is defined by the symbol Z and is calculated by the formula :

For a gas with ideal behavior, molar volume of an ideal gas is equal to the molar volume of a real gas so Z= 1.

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.